1. Field of the Invention
The present invention relates to a digital rights management technology. In particular, the present invention relates to a method and apparatus for efficiently providing a location of a contents encryption key by storing a rights object in a secure multimedia card together with metadata regarding the location of the contents encryption key.
2. Description of the Related Art
Digital rights management (hereinafter, referred to as “DRM”) has been actively studied, and commercial services, to which DRM is applied, have been introduced or are being introduced. DRM is a technical concept to protect digital contents from unauthorized copying and distribution. In the related art, efforts to protect digital contents have been taken, but they have focused on preventing an unauthorized access to the digital contents. For example, an access to the digital contents is permitted to only a user who pays a fee, while a user who does not pay the fee cannot access the digital contents. However, because of the characteristic of digital data, the digital contents can be easily reused, processed, copied, and distributed. Accordingly, if a user who pays a fee and accesses the digital contents copies or distributes the digital contents without authorization, a user who does not pay the fee can use the digital contents. In order to solve this problem, according to the DRM, the digital content is distributed in an encrypted state. In order for a user to use the encrypted digital contents, a license called a rights object (RO) is needed.
Meanwhile, a rights object stored in a host device is moved or copied to a portable storage device. A portable storage device, such as an XD card or a multimedia card, is easily attached and detached to and from a host device, such as a cellular phone, a computer, or a digital camera. The portable storage device does not have the technical limitation in a known hard disk or compact disk. That is, it not only stores data but performs a computing function, such as data control or arithmetic. In addition, a new portable storage device, to which a security function is added to protect digital rights through digital contents storage and transmission/reception, has been developed. Accordingly, the DRM can be used between the portable storage device and the host device. That is, the rights object can be stored in the portable storage device, and the host device can play the encrypted contents using the rights object stored in the portable storage device.
FIG. 1 is an exemplary view showing a process of searching a contents encryption key in a rights object according to the related art. The rights object shown in FIG. 1 can describe rights regarding one or more contents. In order to acquire a contents encryption key of user-desired contents, first, a contents describing portion in the rights object is searched. This corresponds to a portion {circle around (1)} from <o-ex:context> to <o-ex:permission>, which is indicated by a box in FIG. 1. Next, contents identification information (Contents ID) corresponding to the user-desired contents is searched in the contents describing portion {circle around (1)} indicated by the box. This corresponds to a portion {circle around (2)} from <o-dd:uid>ContentID</o-dd:uid> to </o-ex:asset>, which is indicated by another box in FIG. 1. Finally, the contents encryption key is searched in a portion where the searched contents identification information is described. This corresponds to a portion {circle around (3)} where EncryptedCEK is displayed.
However, the process of searching a contents encryption key in a rights object according to the related art has the following problems.
First, even if a specific contents encryption key in the rights object is needed, the rights object may need to be parsed in full until a contents encryption key corresponding to contents identification information is found.
Second, in order to parse the rights object, a parser for a language that describes the corresponding rights object may be needed.
Third, similarly to the play back of contents, when a contents encryption key needs to be extracted in real time, a response speed may be lowered due to unnecessary parsing of the rights object.
Fourth, when a low-performance device, such as a secure multimedia card, follows the above-described search process in order to acquire the contents encryption key of the rights object, it may take a lot of time to parse the rights object, and performance may be degraded.